1. Field of the Invention
The present invention relates to a starting clutch usable in place of a torque converter in an automatic transmission (including an automatic control manual transmission or a sequential manual transmission or the like) of an automobile or the like.
2. Related Background Art
Hitherto, in the automatic transmission, that is AT (automatic transmission), the start of the automobile has been performed by a torque transmission. The torque converter is effective in amplifying the torque and has been mounted on a vast number of AT automobiles because of the smooth torque transmission at the time of increasing or decreasing the torque.
On the other hand, the torque converter has such a drawback as to have a large amount of sliding at the time of increasing or decreasing the torque.
Thus, in recent years, it has been proposed that the starting clutch can be used in place of the torque converter. Further, by reducing a gear ratio and increasing the number of variable speeds, the amplification of the torque at a lower speed range has been attempted.
FIG. 11 is an axial sectional view of the conventional starting clutch. A starting clutch 201 is constituted by combining a damper 245 and a multi-plate clutch 211. The damper 245 has a spring 248. The multi-plate clutch 211 alternately arranges a friction plate 291 attached to an outer periphery of a hub 217 by spline fitting and a separator plate 292 attached to the inner periphery of a clutch case 215 by spline fitting and is supported by a snap ring 312. There is provided a piston 214, which thrusts against the separator plate 292 and the friction plate 291 and is supported to a non-thrust side by a return spring 311. Incidentally, this piston 214 operates by the fact that an oil chamber 256 is supplied with an oil pressure from oil passages 251, 252, 254 and 255.
The starting clutch 201 as described above is constituted in such a manner that the torque is inputted from a connecting portion with an engine output shaft and reaches a case 208 and the damper 245. An impact or a vibration is suctioned by the spring 248 of the damper 245 so as to transmit the torque to the clutch case 215. When the piston 214 operates here, its torque is outputted from the output shaft 240 through the friction plate 291 and the hub 217 from the separator plate 292.
In general, as an alternate of the torque converter of the automatic transmission, the starting clutch is used. The starting clutch is efficient as compared with the torque converter because of direct transmission of the torque. Nevertheless, it has long been pointed that its drawback is that it has no torque amplifying function.